Genetic Codes with No Dedicated Stop Codon: Context-Dependent Translation Termination
Estienne Carl Swart, Valentina Serra, Giulio Petroni, Mariusz Nowackicorrespondenceemail
Publication stage: In Press Corrected Proof
Open access funded by European Research Council
• Alternative nuclear genetic codes continue to be discovered in ciliates
• Genetic codes with stops and all their codons encoding standard amino acids exist
• Transcript ends may distinguish stop codons as such in ambiguous genetic codes
• The ability to resolve genetic code ambiguity may enable genetic code evolution
The prevailing view of the nuclear genetic code is that it is largely frozen and unambiguous. Flexibility in the nuclear genetic code has been demonstrated in ciliates that reassign standard stop codons to amino acids, resulting in seven variant genetic codes, including three previously undescribed ones reported here. Surprisingly, in two of these species, we find efficient translation of all 64 codons as standard amino acids and recognition of either one or all three stop codons. How, therefore, does the translation machinery interpret a “stop” codon? We provide evidence, based on ribosomal profiling and “stop” codon depletion shortly before coding sequence ends, that mRNA 3′ ends may contribute to distinguishing stop from sense in a context-dependent manner. We further propose that such context-dependent termination/readthrough suppression near transcript ends enables genetic code evolution.
Received: August 11, 2015; Received in revised form: April 19, 2016; Accepted: June 6, 2016; Published: July 14, 2016
© 2016 The Author(s). Published by Elsevier Inc.
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